1. Field of the Invention
This invention relates generally to ozonolysis and, more particularly, to a process for the oxidation of unsaturated compounds which is carried out in structured reactors.
2. Background and Related Art
The ozonolysis of olefinic starting materials is among the standard processes of organic chemistry and, accordingly, is comprehensively described in literature and patent specifications, cf., for example, the articles by Naudet and Pasero in Fette, Seifen, Anstrichmittel 62, 1110 (1960), Pryde et al. in J. Org. Chem. 25, 618 (1960) and ibid., 27, 3055 (1962), Moore et al. in J. Americ. Oil. Chem. Soc. 42, 894 (1965), and U.S. Pat. No. 2,813,113 (Goebel et al.). In the first part of the reaction, a gas/liquid reaction of ozone with the olefinic starting material, ozonides are formed as unstable intermediate products. Water-containing substances [DE-OS 2311532] or organic substances [U.S. Pat. No. 5,883,269 (Rebrovic)] are normally added to dilute the olefinic reactants. This is associated on the one hand with the high viscosity of the ozonides formed (cf., Naudet and Pasero in Fette, Seifen, Anstrichmittel 62, op cit) and on the other hand with the control of reactivity [see U.S. Pat. No. 5,883,269]. In the case of organic solvents, substances formed in the subsequent oxidation or reduction of the ozonization products may advantageously be used. The addition of water may be of advantage in terms of suppressing the formation of unwanted secondary products. In the case of oxidative ozonolysis where the ozonization products formed as intermediates are oxidized, ketones or carboxylic acids are formed. The oxidation of the intermediate products is described, for example, in Published International Application WO 95/21809 A1. If the intermediate products are cleaved by reduction, aldehydes are obtained [see German Offenlegungsschrift DE-OS 3440620].
However, the disadvantage of the known processes is that they need improving both in regard to volume/time yield and in regard to selectivity. In addition, in view of the highly exothermic nature of the known processes, uneven temperature stress is encountered time and again in conventional reactors, resulting in variable, not always satisfactory product quality and, above all, product color. Moreover, the danger of hot-spots through inadequate heat dissipation is a safety risk because the ozonization products are unstable and can decompose explosively. Since the dissipation of heat in conventional reactors is limited, the ozone content is generally kept relatively low, typically at around 2% [cf., R. W. Johnson, “Dibasic Fatty Acids in Fatty Acids in Industry”, Marcel Dekker, 1989]. The effect of this is that considerable amounts of gas are circulated and have to be correspondingly purified [DE-AS 1,103,308]. The circulation and treatment of the recycled gas is equipment- and energy-intensive and affects the economy of the process, as does the alternative use of fresh gas for producing the ozone instead of recycling. In order to reduce the risk of spontaneous ignition or explosion in the reactor, air is also used besides high-purity oxygen as the starting gas for producing ozone, which, unfortunately, is a disadvantage in regard to the formation of nitrogen oxides. In addition, carbon dioxide is also used for ozone production [see Published International Application WO 02/064498 A1].
Also, in conventional processes, volatile secondary products are formed to a relatively large extent in both reaction steps, adding considerably to the waste gas burden and again affecting economy.
Accordingly, the complex problem addressed by the present invention was safely, to avoid or reduce the above-mentioned disadvantages of the prior art. More particularly, the invention set out to provide a process which would provide the ozonolysis products in higher volume/time yields and with greater selectivity and which would simplify the technical aspect of the process. Above all, the quantity of ozone in the reaction mixture would be increased, without compromising safety.